Document attachments ==================== .. contents:: Contents: :local: Reasoning --------- The type of a Soledad document's content is `JSON `_, which is good for efficient lookup and indexing. On the other hand, this is particularly bad for storing larger amounts of binary data, because: * the only way to store data in JSON is as unicode string, and this uses more space than what is actually needed for binary data storage. * upon synchronization, the content of a Soledad document needs to be completelly transferred and decrypted for the document to be available for use. Document attachments were introduced as a means to efficiently store large payloads of binary data while avoiding the need to wait for their transfer to have access to the documents' contents. Client-side ----------- In the client, attachments are stored as (SQLite) BLOBs in a separate SQLCipher database. Encryption of data before it's sent to the server is the same used for Soledad documents' content during usual synchronization process (AES-256 GCM mode). See :ref:`client-side-attachment-api` for reference. Usage example ^^^^^^^^^^^^^ The attachments API is currently available in the `Document` class, and the document needs to know about the store to be able to manage attachments. When you create a new document with soledad, that document will already know about the store that created it, and can put/get/delete an attachment: .. code-block:: python from twisted.internet.defer import inlineCallbacks @inlineCallbacks def attachment_example(soledad): doc = yield soledad.create_doc({}) state = yield doc.get_attachment_state() dirty = yield doc.is_dirty() assert state == AttachmentStates.NONE assert dirty == False yield doc.put_attachment(open('hackers.txt')) state = yield doc.get_attachment_state() dirty = yield doc.is_dirty() assert state | AttachmentState.LOCAL assert dirty == True yield soledad.put_doc(doc) dirty = yield doc.is_dirty() assert dirty == False yield doc.upload_attachment() state = yield doc.get_attachment_state() assert state | AttachmentState.REMOTE assert state == AttachmentState.SYNCED fd = yield doc.get_attachment() assert fd.read() == open('hackers.txt').read() Server-side ----------- In the server, a simple REST API is served by a `Twisted Resource `_ and attachments are stored in the filesystem as they come in without modification. A token is used to allow listing, getting, putting and deleting attachments. It has to be added as an HTTP auth header, as in:: Authorization: Token Check out the :ref:`server-side-attachments-rest-api` for more information on how to interact with the server using HTTP. The :ref:`IBlobsBackend ` interface is provided, so in the future there can be different ways to store attachments in the server side (think of a third-party storage, for example). Currently, the :ref:`FilesystemBlobsBackend ` is the only backend that implements that interface. Some characteristics of the :ref:`FilesystemBlobsBackend ` are: * Configurable storage path. * Quota support. * Username, blob_id and user storage directory sanitization.